127. Beware of Fructose!

The original work of Ancel Keys which eventually led to the dietary guidelines recommending a reduction in total fat and particularly saturated fat (SFA) was based on epidemiological studies which related the national fat data to the incidence of heart disease (1). However almost invariably countries which have a high intake of fat also have a high intake of sugar and it is very likely that if this had been the focus of attention, similar associations would have emerged for sugar and heart disease. The work of Keys has been subjected to devastating criticism and in the view of many who have analysed his results it has been totally discredited.

By contrast there is growing evidence that an excessive intake of carbohydrates is a critical factor which contributes to a variety of diseases/conditions which include obesity, hypertension, diabetes and heart disease. This is confirmed by the improvements in health which have been observed by those who make substantial reductions in the amount of carbohydrates in the regular pattern of food consumption.

Recently the spotlight has focussed specifically on sucrose (table sugar) and High Fructose Corn Syrup (HFCS). Sucrose breaks down to a 50:50 mixture of glucose and fructose. HFCS is essentially similar and is widely used in foodstuffs, especially in the USA where there has been a progressive increase in the amount consumed since it was first introduced in the 1970s. Over the next 30 years the fructose consumed in the USA had increased by 30% (2). HFCS-55, which consists of 55% fructose and 42% glucose, is used primarily in sweetened beverages and is also used to sweeten other products (e.g., baked foods and confectionaries).

There are a variety of reasons which taken together make a very compelling case that sugar and HFCS are largely responsible for the deterioration in standards of public health which have been observed in many different countries. The epidemiological evidence shows that there is a close association between the increase in the consumption of these sugars and the increase in the incidence of obesity. Further understanding emerges from a consideration of the different roles of glucose and fructose in the body. At the outset it is crucial to emphasise that although they are very similar in chemical structure they have distinctly different functions and are metabolised by totally different pathways. There is now growing evidence that it is the fructose which is responsible for many of the public health concerns that have arisen in recent years.

In 2002 it was suggested that fructose plays a critical role in the development of Metabolic Syndrome, which is a cluster of diseases/conditions namely obesity, diabetes, hypertension, raised blood triglycerides and low HDL Cholesterol. This was based on evidence from both animal and human studies. In particular when comparisons are made between fructose and sugar (which produces fructose and glucose) it was found that there was greater weight gain, raised blood pressure and raised blood triglycerides with the fructose treatment on its own (3).

Here are some specific examples:

  • The level of triglycerides in the blood was raised when young men were given a diet which was supplemented with 200 g sucrose/day but when the sucrose was replaced with starch, which breaks down to glucose only there was no change(4)
  • In a study conducted in Denmark with healthy men and women aged between 20 and 50 years a comparison was made between supplementation of the regular diet soft drinks containing sucrose and artificial sweeteners. It was found that after 10 weeks the blood pressure had increased in the sugar group but in the other group it had decreased. The body weight increased in the sucrose group but decreased in those using the sweeteners (5)
  • A comparison was done over 8 weeks in which healthy men and women consumed 25% of their energy either as fructose or glucose. Although both groups gained the same amount of weight, those consuming fructose synthesised more fat in the liver and had a greater amount of subcutaneous fat. This is consistent with the fact that virtually all the fructose has to be utilised by the liver which primarily converts it into fat that is stored. The fructose group also had more oxidised LDL Cholesterol and a higher concentration of small dense particles of LDL Cholesterol, both of which are risk factors for heart disease. Insulin sensitivity was reduced in the fructose group but not in those consuming glucose (6).

All of these results provide convincing evidence that fructose is much more damaging to health than glucose. The experimental data fits in very well with the epidemiological information which relates the changes in the incidence of various diseases with the patterns of consumption. There seems very little doubt that increasing consumption of sugar and of HFCS has been the critical factor responsible for the obesity epidemic. Therefore it would be sensible to emphasise the importance of reducing sugar consumption in the advice given to the public. Regrettably because of the obsession with fat and SFA in particular the message is not getting through. Sales of Sugar Sweetened Soft drinks remain at a very high level. Furthermore “low fat” foods continue to be promoted heavily and consumers purchase them in the belief that they are healthy even though the fat taken out has largely been replaced by sugar!!!


  1. A Keys (1970) Circulation 41 (1) pp 188-195
  2. G  A Bray et al (2004) American Journal of Clinical Nutrition 79 (4) pp 537-543
  3. S S Elliott et al (2002) American Journal of Clinical Nutrition 76 (5) pp 911-922
  4. P A Akinynju et al (1968) Nature 218 (5145) pp 975-977
  5. A Raben et al (2002) American Journal of Clinical Nutrition 76 (4) pp 721-729
  6. K Stanhope et al (2009) Journal of Clinical Investigation 119 (5) pp 1322-1334
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